The present invention is directed to active noise control. More particularly, this invention is an active noise control system for canceling or reducing unwanted noise in a closed space.
Active noise control systems are known which use an inverse-phase sound wave to cancel a disturbance. U.S. Pat. No. 4,562,589 to Warnaka et al. entitled xe2x80x9cActive Attenuation of Noise in a Closed Structurexe2x80x9d teaches a system for active attenuation of noise within a closed structure such as an aircraft cabin which operates to introduce a canceling sound wave form (anti-noise) into a closed structure which is responsive to an error signal. The system includes an adaptive filter for updating the cancellation signal sent to the transducers (speakers) to produce the canceling wave form. Although this system was a phenomenal advance for its time, it is somewhat inefficient at reducing noise within the closed space. Furthermore, the components are subject to damage upon large impact loads.
In light of the advantages and drawbacks to the prior art, the present invention is directed to active noise control system for reducing noise within a closed space caused by a source of disturbance such as from a noise and/or vibration source. More particularly, this invention is an efficient active noise control system comprising a reference sensor for deriving a reference signal indicative of a source of disturbance which causes a disturbing noise to be produced in the closed space, an error sensor for sensing a residual sound pressure level and providing a signal indicative thereof to an electronic controller. The electronic controller includes an adaptive filter for providing a canceling signal to a speaker for generating a canceling wave form. The canceling wave form endeavors to cancel the noise caused in the closed space by the source of disturbance. In the present invention, the speakers are inverted in their enclosures and attached directly to the trim of the closed space, thus, providing for more efficient noise cancellation. Preferably, the enclosures are soft-mounted by elastomer isolators or mounts to protect the speaker components from damage to transient loads applied thereto. Each enclosure assembly and installation preferably performs the function of a planar wave guide and constrains the canceling wave form such that it emanates from the confines of the enclosure in a direction which is substantially parallel to the trim""s surface. Further inventive features of the present invention will be apparent from the following detailed description, claims and drawings.